The U.S. patent applications published under the numbers US 2012/0202062 and US 2012/0207846 describe the production of stable amorphous elemental selenium nanoparticles. They are prepared through reaction of a source of selenium with a reducing or oxidizing agent in a liquid medium at a temperature between 0 and 100° C. and in the presence of a macromolecule.
It is written in paragraphs [0047] of the aforementioned applications that the product of the reaction, which can be performed in a liquid medium, is a nanoparticle powder which can be isolated by simply removing the water from the reaction medium. This can be performed by evaporation, filtration or any means obvious to those skilled in the art.